Process for editing of data, in particular with variable channel bit rate

ABSTRACT

For processing data, particularly for transmission via a channel with an specifiably variable data rate, the data are classified into bit classes that are provided with different error redundancy. These bit classes are also weighted with weighting factors. The assignment of the code rates for the bit classes takes place as a function of the respective weighting factors. It is possible to provide a scalable. 
     With the invention, it is possible to realize a scalable channel codec whose configuration is a function solely of the available channel codec bit rate. Such a channel codec is easy to adapt to different transmission techniques.

FIELD OF THE INVENTION

The present invention relates to a method for processing data via achannel with a variable channel bit rate.

BACKGROUND INFORMATION

The standard H 324 M for mobile video telephone applications admits allpossible mobile radio systems so that the requirement for an availabledata rate (channel bit rate) can be different. Even within acommunications system, the available bit rate for speech and videochannel codecs can be different.

German Patent Application No. 41 37 609 describes, a method for decodingbinary signals from binary signals transmitted via a channel andprocessed using an error-correcting code is known. The bit errorprobability is evaluated and a decision made whether the received bitsare correct or errored.

European Patent Application No. 0 643 493 describes an error correctionmethod for a digital cellular radio system. This European PatentApplication describes that data are divided into three different bitclasses with different error protection. For the division into thedifferent bit classes, evaluation of the speech sampled values takesplace based on "A-factor analysis" and using speech intelligibilitytests.

SUMMARY OF THE INVENTION

An adaptation of a channel codec for any transmission method can beachieved.

Unlike conventional transmission methods, a specific channel codec,e.g., a channel codec especially for GSM or DECT, does not need to beprovided for each communications system, e.g., a mobile radio system.The method according to the present invention works reliably even if theavailable channel bit rate is unknown. According to the presentinvention, the configuration of a channel encoder and a correspondingchannel decoder depends only on the available channel codec bit rate.Transmission according to G.723.1 Standard via mobile radio channelswith different channel bit rates is possible without changing thechannel encoder or decoder. The channel encoders or rather decoders onlyneed be designed to be scalable, i.e., the code rate is changed in stepsas a function of the channel bit rate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a block diagram for data processing according to thepresent invention.

FIG. 2 shows exemplary embodiments for a bit distribution among bitclasses and weighting factors of the bit classes.

FIG. 3 shows the bit distribution among the bit classes and a code ratefor different channel bit rates.

FIG. 4 shows another embodiment of the bit distribution for a differenttransmission method.

DETAILED DESCRIPTION

As is shown in FIG. 1, the information bits of a source coder 1 to beprocessed, e.g., according to communications standard G.723.1, arearranged in a unit 2 as a function of their error sensitivity. The mostsensitive bit is placed at the first location of the arranged datastream and the least sensitive bit at the last position. Determinationof the error sensitivity of information bits is based on knownmeasurement techniques that were proposed in conjunction with G.723.1.The data stream arranged in this manner is now divided into differentbit classes c [i] (--block 3--) where, say, i=0, . . . , 4, with c [0]containing the most error-sensitive bits and c [4] the leasterror-sensitive bits. Then, a weighting factor w [i], i=0, . . . , 4(--block 4--) is assigned to each bit class to control the allocation ofthe bit rate (code rate) r for the individual bit classes. The weightingfactor w [i] is chosen as a function of the average error sensitivity ofthe respective bit class c [i]. Here, the code rate r indicates theratio of the number of information bits k to the number of transmissionbits n as described in Furrer, "Fehlerkorrigierende Block-Codierung furdie Datenubertragung", [Error-Correcting Block Encoding for DataCommunications] Birkhauser-Verlag, Basel, 1981, p. 270):

    r=k/n

If r=1, the information bits are transmitted unprotected. For r=1/2,each information bit is provided with a redundant error protection bit.The bits in class 4 receive no protection. Class c [0] contains c [0] -3information bits and three parity check code bits that are added at theend of class c [0] within a data block. The data blocks with thedifferent bit classes are accommodated in a transmission frame. Class c[0] is always provided with the highest error redundancy, e.g., with aminimum error protection rate (code rate r<=1/2). The other classes haveno such high error protection (constraint).

Preferably for transmission, a short parity check code (3-bit paritycheck code) is used that is intended as an error-detecting code in thechannel decoder to detect uncorrected errors (bad frame detection).Particularly when using a Viterbi decoder, the soft decision outputinformation of the SOVA (Soft Decision Viterbi Algorithm) unit 8 can beused for "bad frame detection". With a constraint length of 5 (16states) and a code of the code rate r=1/3, reliable transmission can berealized for an acceptable decoder expense. Higher constraint lengths nolonger lead to a meaningful increase in coding gain. Higher code ratescan be derived from the output code of the 1/3 rate through codepointing. The four bits (tail bits) terminating the code are always putat the end of the last protected bit class and receive the same coderate as this class. This yields a minimum number of channel codec bitsper transmission frame:

    B.sub.min =c[0]+4.

The maximum number of channel codec bits per transmission frame isachieved if all classes have the code rate r=1/3 including errorprotection: ##EQU1##

If B>B_(min) bits are available per transmission frame, in a first passthe average code rates r' [i], i=0, . . . 4 of the classes aredetermined, for example, according to the following equation: ##EQU2##

Here, NINT refers to the rounding to the nearest whole number (integer)For the code rate of bit class zero, the following condition must hold:

    r'[0]<=12/24

The condition ##EQU3## must also be maintained.

To efficiently distribute the channel codec bits, particularly formobile radio applications, an additional redundancy is used for the coderate according to the following equation: ##EQU4##

If with the above equations less bits are assigned for a class thancorresponds to the capacity of a block in the transmission frame, i.e.,this block is not entirely filled up, then in a second pass bits ofclass i (i>1) are transferred into the class i-1 with the next highererror sensitivity until all bits are allocated to the correspondingerror classes.

If more bits are allocated to a bit class than corresponds to thecapacity of its block in the transmission frame, then in the second passbits of class i (i<4) are transferred into the class i+1 until themaximum possible code rate is achieved.

FIG. 2 shows two possible suggestions for the bit distribution and theevaluation with the weighting factors w [i]. The configuration ismodified somewhat. The "tail bits" are in the class with the lowesterror redundancy transmission (this is class 3 since class 4 istransmitted unprotected. . . . The "parity check code bits" for errordetection of the first class are designated with crc.

FIG. 3 shows a table for the specifiably variable data rates (channelbit rates) 8.0, 9.0, 10.0 and 11.4 kbit/s with the bit distribution andthe corresponding code rate r [i]. For other transmission norms, e.g.,according to G.723.1, other bit distributions and code rates arise (seeFIG. 4).

The method according to the present invention is performed particularlyduring a connection setup phase in conjunction with a channel encoder 5and the corresponding channel decoder 7 or each time that the variablechannel bit rate is changed. This is possible theoretically for eachtransmission frame. The communications channel 6 is provided betweenchannel encoder 5 and channel decoder 7. The source decoder 9 followsthe soft decision unit 8.

In the present invention, the assignment of the error redundancy foreach of the bit classes is changed continuously and as a function of thespecifiably variable channel bit rate. The number of redundancy bitsavailable in the transmission frame is thus distributed optimally to thebit classes using an assignment rule, the number of redundancy bit ratesbeing allowed to change in 1-bit steps.

What is claimed is:
 1. A method for processing data to be transmittedvia a channel, the channel having a specifiable variable data rate, themethod comprising the steps of:a) dividing the data into predeterminedbit classes, each of the predetermined bit classes corresponding to arespective error sensitivity; b) weighting the predetermined bit classesusing weighting factors, wherein each of the weighting factors isdetermined as a function of an average error sensitivity of a respectivebit class of the predetermined bit classes; c) providing predeterminederror redundancy data to the predetermined bit classes, wherein at leastone bit class of the predetermined bit classes which has a highestnumber of error-sensitive bits is provided with a higher errorredundancy data of the predetermined error redundancy data; and d)assigning a code rate to a respective bit class of the predetermined bitclasses as a function of a corresponding weighting factor of therespective bit class.
 2. The method according to claim 1, whereinrespective redundancy data of the error redundancy data for each classof the predetermined bit classes is continuously changed as a functionof the specifiable variable data rate.
 3. The method according to claim1, further comprising the step of:e) for each of the predetermined bitclasses, selecting respective redundancy data of the error redundancydata for the at least one bit class so that a bit rate of the respectiveredundancy data is less than or equal to 1/2.
 4. The method according toclaim 3, wherein the bit rate is a ratio of information bits totransmission bits.
 5. The method according to claim 1, furthercomprising the step of:f) for each of the predetermined bit classes,setting respective redundancy data of the error redundancy data, for aparticular bit class of the predetermined bit classes with a lowesterror sensitivity, to zero.
 6. The method according to claim 1, whereinthe predetermined bit classes are provided in a transmission frame in ablock-by-block manner.
 7. The method according to claim 6, wherein, foreach of the predetermined bit classes, respective redundancy data of theerror redundancy data is provided at an end section of a correspondingbit class of the predetermined bit classes in a corresponding block. 8.The method according to claim 6, further comprising the step of:h) whena particular bit class of the predetermined bit classes is not filled toa full capacity of a block in the transmission frame, transferring bitsof the particular bit class having a first error sensitivity to afurther bit class of the predetermined bit classes which has a seconderror sensitivity, the second error sensitivity being higher than thefirst error sensitivity.
 9. The method according to claim 6, furthercomprising the step of:I) when a particular bit class of thepredetermined bit classes has more bits than a full capacity of arespective block in the transmission frame, transferring bits of theparticular bit class which has a first error sensitivity to a furtherbit class with a second error sensitivity, the second error sensitivitybeing lower than the first error sensitivity.
 10. The method accordingto claim 1, further comprising the step of:g) for each of thepredetermined bit classes, increasing respective redundancy data of theerror redundancy data for a corresponding class of the predetermined bitclasses when a predetermined encoding gain is achieved.
 11. The methodaccording to claim 10, wherein, for each of the predetermined bitclasses, the respective redundancy data is provided at an end portion ofa corresponding bit class of the predetermined bit classes in acorresponding block.
 12. The method according to claim 1, wherein stepsa) through d) are executed during a connection setup phase in a channelencoder and in a corresponding channel decoder.
 13. The method accordingto claim 1, wherein steps a) through d) are executed during apredetermined channel bit rate change in a channel encoder and in acorresponding channel decoder.